Water plays an important, life-sustaining role for dialysis patients. When hemodialysis started to blossom over 25 years ago, many dialysis centers used water right from the tap. It is now known that certain contaminants in water supplies can cause severe complications in dialysis patients. In fact, no municipal water can be considered safe for use in hemodialysis applications in the absence of a treatment system, since some of the most toxic contaminants arise from municipal water treatment practices.
Hemodialysis patients are particularly vulnerable to contaminants in the water used to prepare concentrate and dialysis fluid, or in water used for reprocessing dialyzers. This vulnerability stems from the fact that water is the major constituent of dialysis fluid. Compared with individuals who are not on hemodialysis, hemodialysis patients are exposed to extremely large volumes of water. The estimated water intake of a healthy individual is 2 L per day or 14 L per week. By comparison, during a single dialysis treatment lasting four hours, performed at a dialysis fluid flow rate of 800 mL/min, a hemodialysis patient is exposed to 192 L of water, or to 576 L per week, if treated three times weekly.
Furthermore, hemodialysis patients have inadequate barriers to such contaminants. In healthy individuals who are not on dialysis, the gastrointestinal tract separates blood from contaminants in the water. By comparison, the barrier between blood and water in hemodialysis patients is the membrane within the hemodialyzer through which transfer of contaminants is limited only by the molecular or particulate size of the contaminant. As such, the water used for dialysis patients must be of special quality.
Water purification systems are currently used to purify water to a level determined to be safe for dialysis patients. The critical piece of equipment in these water purification systems is the reverse osmosis (RO) machine, which has proven itself to be the safest, most reliable, and most economical method of purifying water for dialysis.
The Association for the Advancement of Medical instrumentation (AAMI) has set forth water standards as guidelines for dialysis centers to follow. These standards list maximum levels for ions found in water as well as for heavy metals and bacteria. Maximum Allowable Levels (mg/L) as set by the AAMI are as follows: Aluminum 0.01, Arsenic 0.005, Barium 0.1, Cadmium 0.001, Total Hardness 21.0, Calcium 2.0, Calcium as CaC03 5.0, Magnesium 4.0, Magnesium as CaC03 16.0, Chlorine (free) 0.5, Chloramine (combined) 0.1, Chromium 0.014, Copper 0.1, Fluoride 0.2, Lead 0.005, Mercury 0.0002, Nitrate (N) 2.0, Potassium 8.0, Selenium 0.09, Silver 0.005, Sodium 70.0, Sulfate 100.0 and Zinc 0.1.
The current trend is to strive for higher purity for dialysis water while keeping operating cost at a minimum. So, the question remains what is the most reliable and economical way to produce water, which meets or exceeds the AAMI standards?